This application is directed to a method and apparatus for the enhanced recovery of liquid hydrocarbons from underground formations. When the rate of hydrocarbon production from an underground formation becomes unacceptably low, various techniques can be used to enhance oil recovery. One method of enhanced oil revovery uses a stream comprising carbon dioxide. The effectiveness of the carbon dioxide as an aid to oil recovery is dependent on its miscibility with the underground oil. By passing carbon dixoide into an underground oil formation at a reservoir pressure above approximately 1,000 psia and a temperature of about 100.degree.-150.degree. F., the carbon dioxide becomes partially miscible with the oil and helps move it toward a well where the hydrocarbon can be produced. The miscibility of the carbon dioxide is dependent upon carbon dioxide purity, oil type, and reservoir pressure and temperature. Contaminants such as nitrogen, oxygen, oxides of nitrogen, carbon monoxide and methane generally are detrimental to such oil miscibility. Therefore, it is desirable that carbon dioxide streams used in enhanced oil recovery be substantially free from such contaminants.
There is abundant literature teaching the various methods of advanced enhanced oil recovery, including those using carbon dioxide. See Carbon Dioxide for the Recovery of Crude Oil, T. Doscher, University of Southern California, DOE Contract ET-78-C-05-5785.
Carbon dioxide can be found naturally occurring in underground formations, often in conjunction with methane and other light hydrocarbons and hydrogen sulfide. In order for such carbon dioxide to be useful in enhanced oil recovery, it is often necessary to purify the carbon dioxide stream, often by absorption, cryogneic separation, or membrane separation techniques such as described in Cooley et al., U.S. Pat. No. 4,130,403. In most cases, naturally occurring carbon dioxide reservoirs are not located near the oil field to be treated, and carbon dioxide pipeline transportation costs can be substantial.
Carbon dioxide can be recovered from crude oil reservoirs which are being subjected to carbon dioxide injection. Depending on well location, time from initial gas injection, and other factors varying amounts of carbon dioxide are recovered along with hydrocarbons from production wells.
Carbon dioxide can also be generated by the combustion of carbonaceous materials such as hydrocarbon as is taught by Holm, U.S. Pat. No. 3,075,918. Holm teaches that the hydrocarbon can be burned in air the combustion products compressed and carbon dioxide selectively absorbed from the combustion products so that a suitably pure carbon dioxide stream is recovered for enhanced oil recovery. Such purification process can be extremely expensive.
Holm, U.S. Pat. No. 3,065,790 teaches the manufacture of carbon dioxide for enhanced oil recovery by the combustion of hydrocarbons. Natural gas or crude oil is burned in air or oxygen. When air is used, a purifying step may be required to remove nitrogen. Holm teaches that noncondensable constituents such as nitrogen do not have a deleterious effect in enhanced oil recovery if they are present in small amounts (less than 5 percent), however they can be tolerated in amounts up to about 20 percent.
It is an object of this invention to provide a method and apparatus for the enhanced recovery of oil.
It is an object of this invention to provide sources of purified carbon dioxide for enhanced oil recovery from underground carbon dioxide which is contaminated with methane, light hydrocarbons, hydrogen sulfide, or mixtures thereof.
It is further an object of this invention to provide a method and apparatus for the manufacture of concentrated carbon dioxide streams which does not require expensive separation of undesirable contaminants such as nitrogen.